Hybrid systems for application in vehicles are known in a number of designs from the prior art. Common in all is that in the drive train at least two different drive units are provided, through which the drive can occur selectively or together. Furthermore, hybrid systems are in general conceived such that at least one of the engines is suitable in deceleration operation, in braking operation, or in combinations thereof, to convert the mechanical energy into a different energy form, for example, into electric energy, and to feed the latter into an accumulator. Such a hybrid system for instance is disclosed in German Patent Publication No. DE 103 10 831 A1. This reference discloses a combined power transmission and drive unit for use in hybrid systems between a first engine and a downstream transmission. The combined power transmission and drive unit includes a power transmission device that can be coupled with the transmission input shaft or includes the device and a clutch device disposed between the device and the engine that establishes or interrupts the power flow from the engine to the power transmission device. Further provided is a second engine in the form of an electric machine, which includes a rotor that can be coupled non-rotatably with the power transmission device. The device is disposed upstream of the power transmission device, viewed in the power flow direction towards the transmission. Furthermore, in the power flow between the switchable clutch device and the first engine, a dual mass flywheel is provided, by which the input is coupled non-rotatably with the crankshaft. The transmission input shaft is mounted on the crankshaft. The electric machine, viewed in axial direction, is disposed around the extension of the switchable clutch device. In addition, the switchable clutch device is disposed quasi within the diameter of the electric machine rotor. The rotor is connected non-rotatably with the housing of the clutch device or it forms an integral unit with the device. The rotor is mounted directly on the housing of the clutch device. This provides a space-saving formation for a hybrid system. Nevertheless, the assembly can be relatively complex in design. A further disadvantage is that the power transmission device and the switchable clutch device constitute devices, which during operation are surrounded by a service fluid or which require a service fluid to realize the mode of operation such that individual components are always covered with the service fluid or rotate in the fluid. Based on the depicted arrangement such that the electric machine is exposed to the service fluid of the two units, the power transmission device and the switchable clutch device, the air gap required for induction between rotor and stator can lead to the impairment of the operating mode. Furthermore, the angular displacements between the engine crankshaft and the transmission input shaft are not adjustable in the depicted form, which is the reason why high demands must be put on the production accuracy of individual components, which makes the overall unit more expensive. A test of individual component's function is possible only after complete assembly of the entire power transmission and drive unit.